1121 - Subsequence

尺取法的应用

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstring>
#include <algorithm>
using namespace std;
const int maxn = 100000 + 7;
const int INF = ~0U >> 1;
int n, S, ans;
int a[maxn];

int main() {
    while(scanf("%d%d", &n, &S) != EOF) {
        memset(a, 0, sizeof(a));
        for(int i = 0; i < n; ++i)
            scanf("%d", &a[i]);
        int left = 0, right = 0;
        ans = INF;
        int sum = a[0];
        for(int i = 0, j = 0; i < n || j < n; ) {
            if(sum < S) {
                if(j < n) {
                    ++j;
                    sum += a[j];
                } else {
                    ++i;
                    sum -= a[i];
                    if(i > j) j = i;
                }
            } else {
                ans = min(ans, j - i + 1);
                //printf("%d %d+++\n", i, j);
                sum -= a[i];
                ++i;
//                printf("%d***\n", sum);
                if(i > j) j = i;
            }
        }
        if(ans == INF) printf("0\n");
        else printf("%d\n", ans);
    }
    return 0;
}